What is the primary function of valve seals?
A 'leak-down' test is the best bet, indicates the place in the process the compression is leaking and if it's across the valve stems than for definite the seals need replacing. Are not able to judge it via the smoke correctly as oil would be slipping previous the rings also.
Valve seals are placed over the intake valve guides so oil will not be drawn into the combustion chamber on intake stroke.
